The initial fuel loading of Japan’s HTTR is currently under way and 17 columns of fuel blocks had been loaded by 10 September as planned. Calculations had indicated that the core would become critical with 17 columns but it did not do so. It is now calculated that it will take 19 or 20 columns. The core is being loaded starting with the outer ring of fuel blocks so that some tests can be done with an annular core.
The outer ring of fuel blocks consists of 18 columns and it will be unfortunate if this configuration is not critical. JAERI staff are evaluating the situation.
There is also discussion going on with the regulator, the Science and Technology Agency, to clarify the maximum temperature limit for the reactor pressure vessel head. However it is expected that fuel loading will resume shortly and criticality should occur at the end of September or early October.